1. Technical Field
The present invention relates to a radiological image detection apparatus for use in a medical X-ray imaging system etc., and a method for manufacturing the same.
2. Related Art
In recent years, a DR (Digital Radiography) using an X-ray image detection apparatus such as an FPD (Flat Panel Detector) for converting X-rays into digital data has been put to practical use. The X-ray image detection apparatus has been being widely used rapidly due to a merit that an image can be confirmed in real time as compared with a background-art CR (Computed Radiography) system using an imaging plate including a photostimulable phosphor (storage phosphor).
Various systems have been proposed for an X-ray image detection apparatus. For example, there is an indirect conversion system in which X-rays are once converted into visible light by a scintillator of CsI:Tl or GOS (Gd2O2S:Tb), and the converted light is converted into electric charges by a semiconductor layer and accumulated (for example, Patent Document 1 (JP-A-2008-51793) and Patent Document 2 (JP-A-2011-17683)).
For example, when such an X-ray image detection apparatus is used for a living body, it is often preferable that the dose of X-rays is low. A scintillator high in amount of luminescence and superior in sensitivity is therefore desired. Addition of an activator to a host of a fluorescent material is known as a method for enhancing the amount of luminescence of the scintillator. In Patent Document 1, description has been made on an X-ray image detection apparatus having a sensor board and a scintillator which includes columnar crystals and on which X-rays are incident from the opposite side to the sensor board, wherein: the density of an activator is increased in an X-ray entrance side region of the scintillator.
Here, the amount of luminescence is increased with increase in the density of the activator on the X-ray entrance side. However, when the region with the increased activator density is distant from a photosensor as in Patent Document 1, MTF (Modulation Transfer Function) deteriorates while absorption of light emitted from the scintillator increases. It is therefore difficult to obtain a sufficient effect in spite of the increase in the activator density.
In addition, when the activator density is enhanced in a region of an early stage of vapor deposition in the scintillator, particularly crystal growth in the scintillator is greatly adversely affected to disorder crystallinity. Light diffused thus among columnar crystals leads to deterioration of MTF.
In addition, the disordered crystallinity leads to deterioration in strength of the scintillator. Particularly when the scintillator is pasted on the sensor board, front end portions of columnar crystals in the scintillator may be damaged due to the load applied to the scintillator in the pasting step. If it is difficult to press the scintillator against the sensor board sufficiently in the pasting step, unevenness may appear in a detected image due to unevenness in adhesion between the sensor board and the scintillator. In order to avoid damage in the pasting step, it may be considered that the temperature of a support during vapor deposition is controlled to flatten the front end portions of the columnar crystals. However, thermal deformation such as warp may occur in the support, to impede the pasting.